This invention relates to an exhaust system for an outboard motor and more particularly to an improved catalytic exhaust system for an outboard motor.
The desirability of catalytic exhaust systems for internal combustion engines to reduce the emission of unwanted exhaust gas constituents to the atmosphere is well known. A particular application where it is desirable to employ such exhaust systems is in connection with outboard motors. With outboard motors, there is a danger that the exhaust gases can pollute not only the atmosphere but the body of water in which the watercraft is operating since most outboard motors employ, as a form of exhaust treatment and silencing, the discharge of the exhaust gases to the atmosphere through the body of water in which the watercraft is operating. With many types of catalysts, it is desirable to position the catalyst bed as close to the exhaust ports of the engine as possible. This is because the temperature there will be the highest and many catalysts require an elevated temperature to promote the treatment of the exhaust gases. However, such close positioning of the catalyst to the exhaust ports does present certain difficulties.
In the first instance, it is difficult to service the catalyst bed when it is positioned in either the cylinder head or cylinder block, whichever forms the exhaust ports for the engine. In addition to this problem, if the catalyst is too close to the exhaust port, then the heat from the catalyst can actually cause damage to the internal components of the engine, particularly the pistons.
It is, therefore, a principal object of this invention to provide an improved and simplified catalytic exhaust system for an internal combustion engine.
It is a further object of this invention to provide an improved catalytic exhaust system for an internal combustion engine when the catalyst bed will be positioned close to the exhaust ports but which will be effectively cooled so as to prevent overheating of the components of the engine.
It is a further object of this invention to provide an improved catalytic exhaust system for an outboard motor that can be easily serviced.